This invention relates to a plasma-addressed liquid crystal display device and more particularly, to the structure of a liquid crystal layer. The invention also relates to a method for fabricating a plasma-addressed liquid crystal device.
Plasma-addressed liquid crystal display devices are disclosed, for example, in U.S. Pat. No. 4,896,149 and U.S. Pat. No. 5,077,553 which corresponds to Japanese Published Unexamined (Kokai) Patent Application No. 1-217396. As shown in FIG. 6, the display device has a built-up flat panel structure which includes a liquid crystal cell 101, a plasma cell 102, and a dielectric sheet 103 intervening therebetween. The plasma cell 102 is formed of a lower glass substrate 104 having grooves 105 each in the form of a stripe on the surface thereof. The grooves 105 extend, for example, along the row of a matrix. The respective grooves 105 are hermetically sealed with the dielectric sheet 103 to establish individually separated discharge channels 106. An ionizable gas is filled in each discharge channel. Protruded portions 107 with which adjacent grooves 105 are separated from each other serve as partition walls defining the individual discharge channels 106. Each groove 105 has a curved bottom at which a pair of discharge electrodes 108, 109 are provided in parallel to each other. These electrodes, respectively, function as an anode and a cathode and act to ionize the gas in the discharge channel, thereby generating a plasma. Such a discharge channel serves as a row scanning unit.
On the other hand, the liquid crystal cell is formed of an upper transparent substrate 110. The substrate 110 is disposed in face-to-face relation with the dielectric sheet 103 through a given space, in which a liquid crystal layer 111 is filled. The substrate 110 is formed with data electrodes 112 on the inner surface thereof. The data electrodes 112 are intersected at right angles with the discharge channels 106 and serve, respectively, as column signal units. Thus, there are established matrix-shaped pixels at the intersected portions of the row signal units and the column scanning units.
In the display device having such a structure as set out hereinabove, the discharge channels 106 are line-sequentially changed over and scanned. In synchronism with the scanning, image signals are applied to the data electrodes 112 provided at the side of the liquid crystal cell 101, thereby performing a display drive. When a plasma is generated within a discharge channel 106 selected through the line-sequential scanning. The inside is substantially uniformly turned into an anode potential, thereby effecting pixel selection in every line. More particularly, the discharge channel 106 functions as a sampling switch. When image signals are applied to individual pixels under conditions where the plasma sampling switch is on, sampling hold is performed thereby controlling whether the pixels are turned on or off. After the plasma sampling switch has been turned off, the image signals are held within the pixels.
FIG. 7 is an enlarged, sectional view of an essential part of the known plasma-addressed liquid crystal display device of FIG. 6. The liquid crystal cell 101 and the plasma cell 102 are separated from each other through the intermediate dielectric sheet 103. An image signal voltage which is applied to a data electrode 112 using the anode potential of a selected discharge channel as a reference is capacitively divided by means of the dielectric sheet 103 and is supplied to the liquid crystal layer 111. In order make a great effective drive voltage, it is necessary that the dielectric sheet 103 be as thin as possible and the thickness is set, for example, at approximately 50 .mu.m. The sheet is so thin that it is difficult to keep the complete flatness of the surfaces. The liquid crystal layer 111 is made, for example, of twisted nematic liquid crystals and should be precisely controlled in thickness within a range of 5 .mu.m.+-.0.5 .mu.m. However, since the flatness of the dielectric sheet 103 is not complete, it is very difficult to uniformly control the gap size of the liquid crystal cell over the entire cell frame. In fact, the gap becomes irregular, with the attendant problem that the quality of the resultant image is impeded. In addition, where the twisted nematic liquid crystal is used, the variation of alignment of the liquid crystal molecules which are caused by application of a voltage is taken out as a variation in quantity of transmitted light. For this purpose, polarizing plates 114, 113 are, respectively, bonded to the outer surfaces of the upper and lower substrates 110, 114. By the provision of a pair of the deflecting plates as set out above, a certain rate of incident light is absorbed therewith, with the problem that the transmittance of the picture cannot be increased.